In mobile communications networks, such as 3GPP networks (3GPP: Third Generation Partnership Project), there is a continuing need for higher data throughput. In order to achieve higher throughputs, various techniques are employed. One approach is to extensively use the limited frequency resources to obtain wide frequency bands for radio communication. This can result in a situation where two or more access nodes communicate over radio interfaces with UEs (UE: user equipment) using at least partially overlapping frequency bands.
If the two or more access nodes use at least partially overlapping frequency bands, spectral interference is likely to occur. Spectral interference can describe a situation where the radio interface between a UE and a first access node is disturbed by a radio interface of a second access node emitting power in the same frequency bands.
Spectral interference can have different effects. One possible effect is a degraded reliability of the radio interface, i.e., a higher probability for lost data packets or radio frames. This may effect the experienced communication quality in an undesired manner voice communication may be disturbed and data communication may be delayed. In certain scenarios, the connection between the UE and the respective access node may even be lost.
A situation of spectral interference can, in particular, occur for so-called heterogeneous networks. In heterogeneous networks, an access node with comparably large coverage, also referred to as macro access node, is supplemented by one or more access nodes of lower power which hence have a smaller coverage (cell size). Latter low-power access nodes are sometimes referred to as pico access nodes and can be deployed closer to the end users, e.g., on street level. Pico access nodes may be situated, preferably, in areas encountering large amounts of data traffic where there is a large demand for capacity. The pico access nodes can then reduce the load imposed on the macro access node and thereby help to increase overall throughput. Often, pico and macro nodes have at least partially overlapping cells.
In heterogeneous networks, a situation where the pico access nodes share the same frequency bands with the macro access nodes often occurs. In particular, a so-called frequency reuse of 1 is often employed where, both, macro and pico access nodes share the entire spectrum to maximize throughput. In other words, different signals may be transmitted via the same frequency band. Due to the overlapping cells, a situation of increased spectral interference may occur.
In case a high speed terminal (UE), i.e. a terminal moving with high speed, connected to a macro cell approaches a small cell the terminal may experience a sudden increase of the interference level. The consequence may be that the UE may not be able to decode any longer the control messages sent by the serving macro cell and the service quality in general is degraded. Therefore, in such a case, the terminal may not be able to perform handover procedures and the radio connection may eventually be broken.
The UEs may loose the connection with serving macro cell before the handover procedures have been executed. Even if the handover can be successfully executed, the UE may suffer from repeated handovers due to the small size of the cells.
In the described situations there is a need to improve the radio link quality between the wireless network and the UE.